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16 January 2023 Fire and Nitrogen Effects on Aristida purpurea Mineral Concentrations
N.A. Dufek, L.T. Vermeire, R.C. Waterman, A.C. Ganguli
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Purple threeawn (Aristida purpurea Nutt.) is a perennial bunchgrass indigenous to much of North America that often dominates disturbed or previously overgrazed rangelands and is mostly avoided by herbivores as forage. Management of threeawn using fire and nitrogen addition can increase its forage quality and likelihood of selection by livestock. We assessed effects of fire, nitrogen fertilizer addition, and phenological stage on purple threeawn mineral concentrations the first growing season postfire on two similar sites in southeastern Montana. Fire (no fire, summer fire, fall fire) and rate of nitrogen fertilizer addition (0, 46, 80 kg N·ha–1) were arranged in a completely randomized, fully factorial design. Samples were collected at five phenological stages throughout each growing season. Minerals were evaluated using laboratory analysis of potassium (K), calcium (Ca), phosphorus (P), sulfur (S), magnesium (Mg), iron (Fe), zinc (Zn), manganese (Mn), and copper (Cu) concentrations. With no nitrogen addition, summer and fall fire increased Ca from 0.22% to 0.38% and 0.31%, respectively, S from 0.08% to 0.15% and 0.13%, and Mg from 0.06% to 0.14% and 0.12%, while fall fire decreased Fe from 289 to 176 ppm. In the vegetative stage, fire (fall and summer averaged) increased K from 0.38% to 1.08%, Ca from 0.22% to 0.35%, P from 0.10% to 0.23%, S from 0.08% to 0.16%, Mg from 0.05% to 0.13%, Zn from 19.2 ppm to 35.8 ppm and Cu from 2.8 ppm to 6.2 ppm. Increasing rate of nitrogen addition and advancing phenological stage had little to no effect on mineral concentrations relative to fire effects. Results indicate prescribed fire can increase mineral concentrations from deficient levels to exceeding requirements for growing cattle, providing more evidence supporting use of prescribed fire to increase forage quality and potential herbivore utilization of purple threeawn within 1 yr following fire.

© 2022 The Society for Range Management. Published by Elsevier Inc. All rights reserved.
N.A. Dufek, L.T. Vermeire, R.C. Waterman, and A.C. Ganguli "Fire and Nitrogen Effects on Aristida purpurea Mineral Concentrations," Rangeland Ecology and Management 86(1), 44-49, (16 January 2023).
Received: 4 May 2023; Accepted: 31 October 2023; Published: 16 January 2023
animal nutrition
prescribed burning
purple threeawn
urea nitrogen fertilizer
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